In a communication network, it is known to synchronize all the network elements to a reference clock signal. Typically, the synchronization is distributed in cascade, according to a master-slave scheme.
In particular, the synchronization is distributed in the form of synchronization information. When a network element receives the synchronization information from another network element, typically it processes them in order to synchronize its local clock, i.e. in order to set the frequency and/or the time of the day of its local clock equal to those of the reference clock signal. Therefore, the network element typically forwards the synchronization information to a further network element.
As known, different synchronization transport protocols can be implemented in order to transport the synchronization information in a communication network. In particular, layer 1 synchronization transport protocols (i.e. synchronization transport protocols wherein the synchronization information is transported at the physical layer of the ISO-OSI model) and layer 2 or 3 synchronization transport protocols (i.e. synchronization transport protocols wherein the synchronization information is transported at the data link and network layers of the ISO-OSI model) are known.
In the case of layer 1 synchronization transport protocols, the synchronization information may be in the form of an analog clock signal, a TDM frame stream (e.g. an E1 frame stream or a T1 frame stream) or a Synchronous Ethernet (SyncE) frame stream. In the first case (i.e. analog clock signal), a network element receiving the synchronization information typically directly uses the received analog clock signal to synchronize its local clock. In the second and third cases, (i.e. TDM frame stream or SyncE frame stream), the network element receives this frame stream and, typically by means of a clock recovery circuitry, it retrieves from the frame stream a clock signal that the network element successively uses to synchronize its local clock.
In the case of layer 2 or 3 synchronization transport protocols, the synchronization information is typically transported in the form of an asynchronous frame stream (e.g. an Ethernet frame stream) wherein each frame comprises a timestamp. An example of these protocols is the known IEEE 1588™-2008 protocol. In this case, a network element receiving an asynchronous frame stream comprising timestamps processes the timestamps and according to them it synchronizes its local clock.
Typically, a network element is configured to support one or more of the synchronization transport protocols cited above. For each supported synchronization transport protocol, the network element typically comprises on its main board a synchronization module which is configured to receive synchronization information in the form provided by that synchronization transport protocol from another network element, to process them in order to synchronize its local clock, and to forward the synchronization information to a further network element. Therefore, the network element typically comprises, on its main board, as many synchronization modules as the supported synchronization transport protocols.
For example, the main board of a network element may comprise a first synchronization module configured to support a first layer 1 synchronization transport protocol wherein the synchronization information are in the form of an analog clock signal, a second synchronization module configured to support a second layer 1 synchronization transport protocol wherein the synchronization information are in the form of a TDM frame stream, a third synchronization module configured to support a third layer 1 synchronization transport protocol wherein the synchronization information are in the form of a SyncE frame stream, and a fourth synchronization module configured to support a layer 2 synchronization transport protocol wherein the synchronization information are in the form of an asynchronous Ethernet frame stream comprising timestamps.
Besides, each synchronization module is provided with a respective cable connector suitable for engaging with a cable (e.g. optical fiber, coaxial cable, twisted pair, etc.) coming from another network element. Typical examples of such connectors are RJ45 connectors or 1.0/2.3 coaxial connectors.